The medicinal leech. A page from the annelids of internal medicine.

Leeches have been used in health care since ancient times by physician and layman alike. As just one of several methods of bloodletting, the leech became the focus of a science that included such subjects as indications, modes of attachment, complications, and relative contraindications. The popularity of leeching has varied immensely over the years. In the 19th century, this annelid saw its numbers decimated because of protean medicinal indications. The leech lost its hold on the practice of medicine in the early 20th century. Recently, the use of leeches has resurged in both the lay and the scientific communities.